5 - 2020 Soybean Management Field Days - Frogeye Leaf Spot Update

Nebraska Soybean Board & Nebraska Extension Author

09/25/2020 Added

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Frogeye Leaf Spot Update with Asha Mane, University of Nebraska Graduate Student

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[00:00:01.109](upbeat music)
[00:00:07.290]Hello. I'm Asha Mane.
[00:00:08.930]I'm currently doing my PhD
[00:00:10.270]at the university of Nebraska, Lincoln.
[00:00:12.840]I joined the department of Plant Pathology,
[00:00:15.050]I work with excision Plant Pathologist,
[00:00:17.480]Dr. Tamra Jackson-Ziems.
[00:00:19.480]and Associate Professor Dr. Sidney Everhart.
[00:00:22.510]Today, I'm going to give you an update
[00:00:24.380]on a very important disease.
[00:00:26.340]Frogeye leaf spot of soybean.
[00:00:29.900]This disease is also known as FLS.
[00:00:33.270]FLS is currently developing in the fields in Nebraska,
[00:00:37.530]and becoming more severe.
[00:00:40.130]This is a good time to scout the field for the disease,
[00:00:43.290]and know whether the fungicide application is needed.
[00:00:47.150]If you have seen FLS in your field last year,
[00:00:50.260]there's a good chance that you will see the disease
[00:00:52.480]this year as well.
[00:00:54.900]FLS is caused by a fungus Cercospora sojina,
[00:00:58.300]and the disease has already been reported
[00:01:00.340]in most Serbian producing areas of the United States.
[00:01:06.230]You can see an leaf image on the right,
[00:01:08.760]that shows symptoms of Frogeye Leaf Spot.
[00:01:12.550]I will show a closer look of this later,
[00:01:15.340]but what you can see here, is tan or gray color lesions,
[00:01:19.920]with red or purple border.
[00:01:23.660]You will see these symptoms mostly
[00:01:25.770]on the leaves in the upper canopy,
[00:01:28.330]but the symptoms can also be seen on seed, stem, pod.
[00:01:35.100]FLS severely affects soybean,
[00:01:38.020]when weather conditions are warm, humid
[00:01:41.200]with frequent rain or irrigation.
[00:01:44.800]Optimal temperature of 77 to 86 degree Fahrenheit
[00:01:49.180]is favorable for the disease.
[00:01:51.590]And if these weather conditions persist,
[00:01:54.620]that might make the disease severe.
[00:01:59.680]By scouting for Frogeye Leaf Spot,
[00:02:02.690]what you will see is,
[00:02:05.240]the spots initially look like water spots,
[00:02:08.420]which later turned into lesions.
[00:02:11.980]When the lesions are younger, they're smaller in size,
[00:02:15.750]but as they grow older, they get bigger.
[00:02:20.630]By scouting for FLS,
[00:02:23.120]it is also important to know that,
[00:02:24.860]some other soybean diseases may look like FLS.
[00:02:29.230]One of the examples is Phyllosticta Leaf Spot.
[00:02:33.610]This disease is caused by a different fungus
[00:02:36.120]Phyllosticta sojicola.
[00:02:38.780]As you can see, in the image on the left,
[00:02:41.800]Phyllosticta Leaf Spots are also tan or gray in color,
[00:02:46.240]they have dark borders and are circular to oval in shape.
[00:02:51.640]But, what makes Phyllosticta Leaf Spots different,
[00:02:54.890]is once these lesions mature,
[00:02:58.290]they show black specks in the middle of the spot.
[00:03:02.370]This black specks, are fungal reproductive structures,
[00:03:06.310]and these will not be seen in case of FLS.
[00:03:10.490]When you look at Frogeye Leaf Spot,
[00:03:12.260]you will see tan or gray Legion with red or purple border.
[00:03:17.620]And a very characteristic black spot at the center,
[00:03:21.270]which gives the spots and appearance of an eye of a frog.
[00:03:27.120]Moving on to management strategies,
[00:03:30.340]the general management strategies for FLS
[00:03:32.880]are selection of resistant varieties,
[00:03:36.490]avoiding growing continuous soybean crop,
[00:03:39.270]and application of foliar fungicides.
[00:03:42.930]Foliar fungicide application should be done
[00:03:45.170]only after scouting.
[00:03:47.180]And it should be done at a stage,
[00:03:49.110]which is most effective for the efficacy.
[00:03:53.570]Fungicide application is most effective,
[00:03:55.940]when it is done at reproductive stage R3,
[00:03:59.380]to reproductive stage R5.
[00:04:02.060]R3 is beginning of seed development,
[00:04:05.020]and R5, is beginning of pod development.
[00:04:10.330]For the fungicide treatment of Frogeye Leaf Spot,
[00:04:12.790]there are three classes of fungicides
[00:04:15.010]typically used on soybean.
[00:04:17.360]First is QoI or more commonly known as
[00:04:20.870]strobilurin group of fungicides.
[00:04:23.260]They belong to Frac Group 11.
[00:04:25.410]DMI fungicides, belong to Frac Group 3,
[00:04:29.540]and SDHI fungicides that belong to Group 7.
[00:04:34.320]If you wish to know more information about this,
[00:04:36.960]we should definitely refer to the disease management section
[00:04:40.400]from 2020 guide for weed, disease,
[00:04:43.040]and insect management in Nebraska.
[00:04:46.640]Another very useful resource for you,
[00:04:49.110]could be an article that was published
[00:04:51.000]in Crop Protection Network.
[00:04:53.260]This article discusses fungicide efficacy,
[00:04:56.550]for control of soybean foliar diseases.
[00:05:00.090]If you use the given QR code,
[00:05:02.450]or if you go to the given URL,
[00:05:04.590]you will find a link to this article.
[00:05:07.050]In case you do not have ac6cess to this article,
[00:05:09.340]don't worry about it, because later in this talk,
[00:05:11.990]I will talk in detail about the fungicide efficacy.
[00:05:17.610]Looking at the foliar fungicides for FLS treatment,
[00:05:21.750]I already mentioned the three classes
[00:05:23.850]that are typically used.
[00:05:26.220]But QoI fungicides, from Group 11,
[00:05:29.180]are historically known to be most effective to treat FLS.
[00:05:34.100]But the issue is the resistance is becoming more common.
[00:05:38.510]Development of resistance,
[00:05:40.010]reduces the efficacy of the fungicide.
[00:05:45.260]QoI fungicide resistance,
[00:05:46.970]has already been reported in the United States.
[00:05:50.880]You can see in this map, that from year 2010 to 2017,
[00:05:56.220]240 counties from 14 different States,
[00:05:59.520]reported QoI fungicide resistance.
[00:06:04.060]In late 2018,
[00:06:06.830]resistance was confirmed in four counties
[00:06:09.010]in Southeast, South Dakota.
[00:06:11.890]In the state of Iowa,
[00:06:14.270]samples from 73 fields in 51 counties
[00:06:18.250]were found to be resistant to QoI fungicides.
[00:06:23.310]And for the most important update of the day,
[00:06:26.540]in year 2019, QoI fungicide resistance,
[00:06:30.260]was confirmed for the first time in the state of Nebraska.
[00:06:34.660]We conducted a small survey,
[00:06:36.420]where FLS samples were collected from 10 Nebraska counties.
[00:06:41.510]These 10 counties that are highlighted yellow in this map.
[00:06:45.840]98% of the collected samples,
[00:06:48.740]were found to be resistant to QoI fungicides.
[00:06:53.890]Since these were the only 10 counties
[00:06:55.950]from where samples were collected,
[00:06:58.960]we currently do not know how widespread
[00:07:01.480]this problem is in Nebraska,.
[00:07:04.240]But, to avoid the possible widespread,
[00:07:07.810]draws should update their management strategies.
[00:07:11.800]Draws should opt for an integrated management plan,
[00:07:14.720]which includes, selection of resistant varieties,
[00:07:20.350]practicing crop rotation, whenever possible,
[00:07:24.590]and application of foliar fungicides.
[00:07:28.480]To give you an update on fungicide efficacy,
[00:07:31.250]for control of soybean foliar diseases.
[00:07:34.180]You can see this table,
[00:07:36.420]this table is taken
[00:07:37.820]from the fungicide efficacy
[00:07:39.500]the source I earlier talked about.
[00:07:42.410]Though, there's a lot of information on this table,
[00:07:44.580]I'm going to highlight the information
[00:07:46.670]that is relevant for you.
[00:07:49.470]The QoI or strobilurin group of fungicides,
[00:07:52.460]when used alone for treatment of FLS,
[00:07:55.290]they showed poor efficacy.
[00:07:57.730]Also, the SDHR group of fungicides,
[00:07:59.760]when used alone to treat FLS showed poor efficacy.
[00:08:03.840]Which means these group of fungicides
[00:08:06.100]are no longer efficient for a FLS treatment.
[00:08:11.610]But DMI group of fungicides and MBC thiophanates,
[00:08:16.070]when used alone, showed fair, good, or very good efficacy.
[00:08:21.020]So this could be a better option.
[00:08:25.960]Looking at the efficacy of mixed mode of action fungicides,
[00:08:30.160]there are different products available,
[00:08:33.080]and this product show fair, good, or very good efficacy.
[00:08:39.510]Some of the mixed mode of action fungicides
[00:08:41.730]are now available in a combination of three,
[00:08:44.930]or you can also make your own mixes.
[00:08:48.380]But if you are making your own combinations,
[00:08:50.820]be sure of following the pesticide label instructions.
[00:08:56.190]If you're wondering,
[00:08:57.240]how do you know if there is a fungicide resistance
[00:08:59.590]in your field.
[00:09:01.180]You can submit the FSL samples to UNL diagnostics clinic.
[00:09:05.800]You can use the given QR code or visit the given URL,
[00:09:10.510]which will provide all the information
[00:09:12.730]on how to collect the samples and how to submit them
[00:09:16.440]to UNL diagnostics clinic.
[00:09:20.179]At the unit department of plant pathology,
[00:09:22.740]we are currently developing a rapid test,
[00:09:25.100]to detect fungicide resistance to the QoI group.
[00:09:29.330]This test is currently in progress.
[00:09:32.090]The samples that will be collected now,
[00:09:34.600]will be processed in winter.
[00:09:37.250]But once this test is established,
[00:09:39.160]we will be able to perform it in two to three hours.
[00:09:43.170]We will be able to perform this test,
[00:09:45.000]both in lab and in field.
[00:09:47.460]And this test is going to allow us,
[00:09:49.470]the timely suggestion for the fungicide selection.
[00:09:53.560]If you wish to know more information,
[00:09:56.280]these are some very useful resources you can find online.
[00:10:00.580]If you want to stay updated
[00:10:02.000]on disease management in Nebraska,
[00:10:04.210]do follow us on Twitter.
[00:10:07.360]Thank you.

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5 - 2020 Soybean Management Field Days - Frogeye Leaf Spot Update

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